Credit

Caption

Bone marrow. Coloured Scanning Electron Micrograph (SEM) of spongy bone filled with bone marrow. This is the region of the shaft of a long bone. Here, a bony network of trabeculae (yellow) makes up spongy bone, separated by spaces. Inside these spaces is bone marrow (red). Bone marrow contains stem cells which, through a process known as haemopoiesis, generate the three main types of cells found in the blood: red blood cells (erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes). Bone marrow in human limb bones is replaced by fat cells later on in life. Magnification: x50 at 6x7cm size.